The purpose of the study is to compare the safety and efficacy of Dapsone and Atovaquone in the prevention of Pneumocystis carinii pneumonia (PCP) in HIV-infected patients who are at high risk for PCP and who are intolerant of trimethoprim and/or sulfonamides. This is a multicenter, randomized, comparative study of two prophylactic regimens (daily dapsone and daily atovaquone). Patient accrual is expected to take 12 months, with follow-up being conducted for at least 20 months. The average follow-up period is expected to be 24 months. The duration of the study will be approximately 32 months.